A torque fluctuation absorber is arranged on a power transmission path between an engine and a transmission, and absorbs (restricts) fluctuating torque generated between the engine and the transmission. The torque fluctuation absorber may include a damper portion for absorbing the fluctuating torque by means of an elastic force (a spring force). The damper portion includes a coil spring arranged between the rotating members in a circumferential direction thereof so that the coil spring absorbs the fluctuating torque by being compressed in a case where the two rotating members rotate relative to each other.
A device provided with the aforementioned damper portion is disclosed in JP2010-255753A (hereinafter referred to as Patent reference 1). The device disclosed in Patent reference 1 includes a first rotating member connected to a crankshaft, a second rotating member connected to a torque converter, an outer side damper supporting member connected to the first rotating member, an inner side damper supporting member connected to the second rotating member and a coil spring arranged between the outer side damper supporting member and the inner side damper supporting member. According to the device disclosed in Patent reference 1, the outer side damper supporting member is connected the first rotating member via a block member and a bolt which are arranged radially outwardly relative to the coil spring.
Another device is disclosed in JP2010-91100A (hereinafter referred to as Patent reference 2). The device disclosed in Patent reference 2 includes a spring holding member connected to a crankshaft, a spring side member connected to a torque converter and a damper spring arranged between the spring holding member and the spring side member. According to the device disclosed in Patent reference 2, the spring side member is connected to the torque converter via a set block and a fastening bolt each of which is arranged at a position offset from the damper spring in a circumferential direction.
According to the damper portion of Patent reference 1, however, the coil spring is arranged radially inwardly relative to the block member, and therefore a torsional angle of the damper portion may be small. Thus, flexibility in or a degree of freedom of improvement in performance, which is attained by setting a torsional rigidity at low, may be decreased.
According to the damper portion of Patent reference 2, the spring holding member arranged at an engine side relative to the damper spring on the power transmission path has a small inertia, and thus a resonance frequency is high. Accordingly, attenuation performance may not be sufficiently ensured.
A need thus exists for a torque fluctuation absorber which is not susceptible to the drawback mentioned above.